Lubricating oil composition for internal combustion engine

ABSTRACT

A lubricating oil composition for an internal combustion engine including: (A) a lubricant base oil having a kinematic viscosity at 100° C. of 2 to 5 mm 2 /s; (B) a metallic detergent in an amount of 500 to 2500 mass ppm in terms of Ca and 100 to 1000 mass ppm in terms of Mg, on the basis of the total mass of the composition, the metallic detergent including both (B1) a Ca-containing metallic detergent and (B2) a Mg-containing metallic detergent; (C) a boron-containing additive in an amount of 50 to 1000 mass ppm in terms of boron on the basis of the total mass of the composition, wherein the boron-containing additive is oil-soluble or oil-dispersible and is stable in oil, and wherein the boron-containing additive may compose at least a part of the component (B); and (D) an oil-soluble organic Mo compound in an amount of 100 to 2000 mass ppm in terms of Mo on the basis of the total mass of the composition, wherein a mass ratio (MB/Mg) of boron content of the composition (MB) to Mg content of the composition (Mg) is 0.5 to 10.

FIELD

The present invention relates to lubricating oil compositions forinternal combustion engines.

BACKGROUND

Recent years, it has been proposed to replace conventional naturallyaspirated engines with smaller displacement engines having turbochargers(turbocharged downsized engines) for the purpose of reducing fuelconsumption of internal combustion engines for automobiles, especiallyof gasoline engines for automobiles. Using turbocharged downsizedengines with turbochargers makes it possible to reduce displacementwhile output power is kept, and to achieve low fuel consumption.

On the other hand, a phenomenon that a cylinder has ignition prior topredetermined timing (LSPI: Low Speed Pre-Ignition) may occur in aturbocharged downsized engine when torque is increased in a low rotationspeed range. LSPI causes more energy loss, which limits improvement offuel consumption and increase of low speed torque. Engine oil issuspected of influencing the occurrence of LSPI. These days, engine oilincluding Ca-based detergent and Mg-based detergent together is proposedin order to secure detergency while controlling LSPI. However, the fuelefficiency of such engine oil is not ensured yet or is insufficient.

CITATION LIST Patent Literature

Patent Literature 1: JP 2011-140572 A

Patent Literature 2: JP 2013-159734 A

Patent Literature 3: WO 2015/114920 A1

Patent Literature 4: WO 2015/171292 A1

Patent Literature 5: WO 2015/171978 A1

Patent Literature 6: WO 2015/171980 A1

Patent Literature 7: WO 2015/171981 A1

SUMMARY Technical Problem

An object of the present invention is to provide a lubricating oilcomposition for an internal combustion engine that can secure LSPIsuppression performance and detergency, and improve fuel efficiency atthe same time.

Solution to Problem

A lubricating oil composition for an internal combustion engine of thepresent invention comprises: (A) a lubricant base oil having kinematicviscosity at 100° C. of 2 to 5 mm²/s; (B) a metallic detergent in anamount of 500 to 2500 mass ppm in terms of calcium and 100 to 1000 massppm in terms of magnesium, on the basis of the total mass of thecomposition, the metallic detergent comprising both (B1) acalcium-containing metallic detergent and (B2) a magnesium-containingmetallic detergent; (C) a boron-containing additive in an amount of 50to 1000 mass ppm in terms of boron on the basis of the total mass of thecomposition, wherein the boron-containing additive is oil-soluble oroil-dispersible and is stable in oil, and wherein the boron-containingadditive may compose at least a part of the component (B); and (D) anoil-soluble organic molybdenum compound in an amount of 100 to 2000 massppm in terms of molybdenum on the basis of the total mass of thecomposition, wherein a mass ratio (MB/Mg) of boron content of thecomposition (MB) to magnesium content of the composition (Mg) is 0.5 to10; and the composition satisfies one or more requirement selected fromthe following (i) to (iii):

(i) the boron content of the composition is no less than 270 mass ppm onthe basis of the total mass of the composition;

(ii) the component (C) comprises a boric acid salt-overbased metallicdetergent, wherein the boric acid salt-overbased metallic detergent maycompose at least a part of the component (B1) or the component (B2) orthe combination thereof; and

(iii) the mass ratio (MB/Mg) of the boron content of the composition(MB) to the magnesium content of the composition (Mg) is no less than0.8.

In this specification, “kinematic viscosity at 100° C.” means kinematicviscosity at 100° C., which is specified by ASTM D-445; and “HTHSviscosity at 150° C.” means viscosity at a high shear rate and hightemperature at 150° C., which is specified by ASTM D4683.

Concerning the component (C), that the boron-containing additive “maycompose at least a part of the component (B)” means that thisboron-containing additive may either compose at least a part of thecomponent (B), or be an additive that is not the component (B).

Concerning the requirement (ii), that the boric acid salt-overbasedmetallic detergent “may compose at least a part of the component (B1) orthe component (B2) or the combination thereof” means that this metallicdetergent may compose at least a part of the component (B1), compose atleast a part of the component (B2), compose at least a part of thecomponent (B1) and at least a part of the component (B2), or be ametallic detergent that is not the component (B1) or the component (B2).When the requirement (ii) is satisfied, the boric acid salt-overbasedmetallic detergent contributes to both the content of the component (C)and the content of the component (B).

When the requirement (iii) is satisfied, the range of the mass ratio ofthe composition MB/Mg corresponds to a logical product of the range 0.5to 10 and the range specified in the requirement (iii) “no less than0.8”, that is, 0.8 to 10.

Advantageous Effects of Invention

The lubricating oil composition for an internal combustion engine of thepresent invention makes it possible to secure LSPI suppressionperformance and detergency, and to improve fuel efficiency at the sametime.

DETAILED DESCRIPTION OF EMBODIMENTS

The present invention will be described hereinafter. Expression “A to B”concerning numeral values A and B means “no less than A and no more thanB” unless otherwise specified. In such expression, if a unit is addedonly to the numeral value B, the same unit is applied to the numeralvalue A as well. A word “or” means a logical sum unless otherwisespecified.

<(A) Lubricant Base Oil>

In the lubricating oil composition of the present invention, a lubricantbase oil of 2 to 5 mm²/s in kinematic viscosity at 100° C. (hereinaftermay be referred to as “lubricant base oil according to this embodiment”)is used as a base oil.

Examples of the lubricant base oil according to this embodiment includeparaffinic mineral oils, paraffinic base oils, isoparaffinic base oils,and mixtures thereof having a kinematic viscosity at 100° C. of 2 to 5mm²/s, which are obtained by refining lubricant oil fractions that areobtained by atmospheric distillation and/or vacuum distillation of crudeoils, through one or more refining processes selected from solventdeasphalting, solvent extraction, hydrocracking, solvent dewaxing,catalytic dewaxing, hydrorefining, sulfuric acid washing, claytreatment, etc.

Preferred examples of the lubricant base oil according to thisembodiment include a base oil, a row material of which is any of thefollowing base oils (1) to (8), and which is obtained by recoveringlubricant oil fractions derived from refining, through a predeterminedrefining method, oil of the row material and/or lubricant oil fractionsrecovered from the oil of the row material:

(1) a distillate obtained by atmospheric distillation of paraffin basecrude oils and/or mixed base crude oils;

(2) a distillate obtained by vacuum distillation of residual oils ofparaffin base crude oils and/or mixed base crude oils (WVGO);

(3) a wax obtained through a lubricant oil dewaxing process (slack waxetc.) and/or synthetic wax obtained through a gas to liquid (GTL)process or the like (Fischer-Tropsch wax, GTL wax, etc.);

(4) a mixed oil of at least one selected from the base oils (1) to (3)and/or a mild hydrocracked oil of the mixed oil;

(5) a mixed oil of at least two selected from the base oils (1) to (4);(6) a deasphalted oil of the base oil (1), (2), (3), (4) or (5) (DAO);

(7) a mild hydrocracked oil of the base oil (6) (MHC); and

(8) a mixed oil of at least two selected from the base oils (1) to (7).

Preferred examples of the above described predetermined refining methodinclude hydrorefining such as hydrocracking and hydrofinishing; solventrefining such as furfural solvent extraction; dewaxing such as solventdewaxing and catalytic dewaxing; clay refining by acid clay, activatedclay, etc.; and chemical (acid or alkali) washing such as sulfuric acidwashing and caustic soda washing. In the present invention, theserefining methods may be carried out individually, or at least tworefining methods may be carried out in combination. When at least tworefining methods are combined, the order thereof is not restricted, andcan be suitably determined.

The following base oil (9) or (10) is especially preferable as thelubricant base oil according to this embodiment. The base oils (9) and(10) are obtained by carrying out a predetermined process on a base oilselected from the base oils (1) to (8), or on lubricant oil fractionsrecovered from any of the base oils (1) to (8):

(9) a hydrocracked base oil obtained by: hydrocracking a base oilselected from the base oils (1) to (8), or lubricant oil fractionsrecovered from any of the base oils (1) to (8); carrying out a dewaxingprocess such as solvent dewaxing and catalytic dewaxing on the productsthereof, or lubricant oil fractions recovered from the products thereofby distillation or the like; and optionally further distilling theproducts thereof after the dewaxing process; and

(10) a hydroisomerized base oil obtained by: hydroisomerizing a base oilselected from the base oils (1) to (8), or lubricant oil fractionsrecovered from any of the base oils (1) to (8); carrying out a dewaxingprocess such as solvent dewaxing and catalytic dewaxing on the productsthereof, or lubricant oil fractions recovered from the products thereofby distillation or the like; and optionally further distilling theproducts thereof after the dewaxing process. A catalytic dewaxingprocess is preferable as the dewaxing process.

When obtaining the above described lubricant base oil (9) or (10), asolvent refining process and/or hydrofinishing process may be furthercarried out at a suitable stage if necessary.

A catalyst used for the above described hydrocracking orhydroisomerization is not restricted, but a hydrocracking catalystcomprising a metal having hydrogenating ability (such as at least onemetal in the VIa group and VIII group of the periodic table) supportedon a composite oxide having cracking activity (for example,silica-alumina, alumina-boria and silica zirconia), or on at least oneof the composite oxides in combination, bound by binders, as a support;or a hydroisomerization catalyst comprising at least one metal havinghydrogenating ability including at least one group VIII metal supportedon a support including zeolite (such as ZSM-5, zeolite beta, andSAPO-11) is preferably used. A hydrocracking catalyst andhydroisomerization catalyst may be used in combination by laminating ormixing or the like.

Reaction conditions of hydrocracking and hydroisomerization are notrestricted. Preferably, the hydrogen partial pressure is 0.1 to 20 MPa,the average reaction temperature is 150 to 450° C., LHSV is 0.1 to 3.0hr⁻¹, and the hydrogen/oil ratio is 50 to 20000 scf/b.

The kinematic viscosity of the lubricant base oil according to thisembodiment at 100° C. is 2.0 to 5.0 mm²/s, preferably no more than 4.5mm²/s, more preferably no more than 4.4 mm²/s, and especially preferablyno more than 4.3 mm²/s; and preferably no less than 3.0 mm²/s, morepreferably no less than 3.5 mm²/s, further preferably no less than 3.8mm²/s, and especially preferably no less than 4.0 mm²/s. If thekinematic viscosity of the lubricant base oil at 100° C. is more than5.0 mm²/s, low-temperature viscosity properties of the lubricating oilcomposition may deteriorate, and the fuel efficiency might beinsufficient. If the kinematic viscosity thereof is less than 2.0 mm²/s,oil film formation at lubricating points might be insufficient, whichcauses poor lubricity, and evaporation loss of the lubricating oilcomposition might be large.

The kinematic viscosity of the lubricant base oil according to thisembodiment at 40° C. is preferably no more than 40 mm²/s, morepreferably no more than 30 mm²/s, further preferably no more than 25mm²/s, especially preferably no more than 22 mm²/s, and most preferablyno more than 20 mm²/s. On the other hand, the kinematic viscositythereof at 40° C. is preferably no less than 10 mm²/s, more preferablyno less than 14 mm²/s, further preferably no less than 16 mm²/s,especially preferably no less than 18 mm²/s, and most preferably no lessthan 19 mm²/s. If the kinematic viscosity of the lubricant base oil at40° C. is more than 40 mm²/s, low-temperature viscosity properties ofthe lubricating oil composition may deteriorate, and the fuel efficiencymight be insufficient. If the kinematic viscosity thereof is less than10 mm²/s, oil film formation at lubricating points might beinsufficient, which causes poor lubricity, and evaporation loss of thelubricating oil composition might be large.

In this specification, “kinematic viscosity at 40° C.” means kinematicviscosity at 40° C. specified by ASTM D-445.

The viscosity index of the lubricant base oil according to thisembodiment is preferably no less than 100, more preferably no less than110, further preferably no less than 120, especially preferably no lessthan 125, and most preferably no less than 130. If the viscosity indexthereof is less than 100, not only viscosity-temperaturecharacteristics, thermal and oxidation stability and anti-evaporationperformance deteriorate, but also the friction coefficient tends toincrease and anti-wear properties tends to decrease. The viscosity indexin this specification means a viscosity index measured conforming to JISK 2283-1993.

The density of the lubricant base oil according to this embodiment at15° C. (

₁₅) is preferably no more than 0.860, more preferably no more than0.850, further preferably no more than 0.840, and especially preferablyno more than 0.835. The density at 15° C. in this specification meansdensity measured at 15° C., conforming to JIS K 2249-1995.

The pour point of the lubricant base oil according to this embodiment ispreferably no more than −10° C., more preferably no more than −12.5° C.,further preferably no more than −15° C., especially preferably no morethan −17.5° C., and most preferably no more than −20.0° C. If the pourpoint is beyond the above described upper limit, low-temperaturefluidity of whole of the lubricating oil composition tends todeteriorate. The pour point in this specification means a pout pointmeasured conforming to JIS K 2269-1987.

The sulfur content in the lubricant base oil according to thisembodiment depends on the sulfur content in its raw material. Forexample, in a case where a substantially sulfur-free raw material suchas a synthetic wax component obtained through Fischer-Tropsch reactionor the like, is used, a substantially sulfur-free lubricant base oil canbe obtained. In a case where a raw material containing sulfur, such as aslack wax obtained through the process of refining the lubricant baseoil, and a microwax obtained through a wax refining process, is used,the sulfur content in the obtained lubricant base oil is usually no lessthan 100 mass ppm. In the lubricant base oil according to thisembodiment, in view of further improvement of the thermal and oxidationstability and reduction of the sulfur content, the sulfur content ispreferably no more than 100 mass ppm, more preferably no more than 50mass ppm, further preferably no more than 10 mass ppm, and mostpreferably no more than 5 mass ppm.

The nitrogen content in the lubricant base oil according to thisembodiment is preferably no more than 10 mass ppm, more preferably nomore than 5 mass ppm, and further preferably no more than 3 mass ppm. Ifthe nitrogen content is beyond 10 mass ppm, the thermal and oxidationstability tends to deteriorate. The nitrogen content in thisspecification means nitrogen content measured conforming to JIS K2609-1990.

Preferably, % C_(P) of the lubricant base oil according to thisembodiment is no less than 70, more preferably no less than 80, andfurther preferably no less than 85; and usually no more than 99,preferably no more than 95, and more preferably no more than 94. In acase where % C_(P) of the lubricant base oil is under the above lowerlimit, the viscosity-temperature characteristics, thermal and oxidationstability and friction properties tend to deteriorate, and effects of anadditive tend to decrease when the additive is incorporated to thelubricant base oil. In a case where % C_(P) of the lubricant base oil isbeyond the above upper limit, solubility of an additive tends todecrease.

Preferably, % C_(A) of the lubricant base oil according to thisembodiment is no more than 2, more preferably no more than 1, furtherpreferably no more than 0.8, and especially preferably no more than 0.5.In a case where % C_(A) of the lubricant base oil is beyond the aboveupper limit, the viscosity-temperature characteristics, thermal andoxidation stability and fuel efficiency tend to deteriorate.

Preferably, % C_(N) of the lubricant base oil according to thisembodiment is no more than 30, more preferably no more than 25, furtherpreferably no more than 20, and especially preferably no more than 15.Preferably, % C_(N) of the lubricant base oil is no less than 1, andmore preferably no less than 4. In a case where % C_(N) of the lubricantbase oil is beyond the above upper limit, the viscosity-temperaturecharacteristics, thermal and oxidation stability and friction propertiestend to deteriorate. In a case where % C_(N) thereof is under the abovelower limit, solubility of an additive tends to decrease.

In this specification, % C_(P), % C_(N) and % C_(A) mean percentage ofthe paraffin carbon number to all the carbon atoms, percentage of thenaphthene carbon number to all the carbon atoms, and percentage of thearomatic carbon number to all the carbon atoms, respectively, obtainedby the method conforming to ASTM D 3238-85 (n-d-M ring analysis). Thatis, the above described preferred ranges of % C_(P), % C_(N), and %C_(A) are based on values obtained according to the above method. Forexample, the value of % C_(N) obtained according to the above method canindicate more than 0 even if the lubricant base oil does not containnaphthenes.

The saturated content in the lubricant base oil according to thisembodiment is preferably no less than 90 mass %, more preferably no lessthan 95 mass %, and further preferably no less than 99 mass %, on thebasis of the total mass of the lubricant base oil. The proportion of thecyclic-saturated content to the saturated content is preferably no morethan 40 mass %, preferably no more than 35 mass %, preferably no morethan 30 mass %, more preferably no more than 25 mass %, and furtherpreferably no more than 21 mass %. The proportion of the cyclicsaturated content to the saturated content is also preferably no lessthan 5 mass %, and more preferably no less than 10 mass %. The saturatedcontent and the proportion of the cyclic-saturated content to thesaturated content within the above range makes it possible to improvethe viscosity-temperature characteristics, and thermal and oxidationstability. In a case where an additive is incorporated to the lubricantbase oil, functions of the additive can be brought out at a higher levelwhile the additive is sufficiently stably dissolved and retained in thelubricant base oil. Further, friction properties of the lubricant baseoil itself can be improved, and as a result, friction-reducingperformance can be improved, which leads to improvement of the energyefficiency. In this specification, the saturated content means a valuemeasured conforming to ASTM D 2007-93.

Any of similar methods from which the same results are obtained can beused for each of a method of separating the saturated content, and thecomposition analysis of e.g. the cyclic saturated content, and thenoncyclic saturated content. Examples thereof include the above methodspecified in ASTM D 2007-93, the method specified in ASTM D 2425-93, themethod specified in ASTM D 2549-91, methods using high performanceliquid chromatography (HPLC), and methods obtained by improving thesemethods.

The aromatic content in the lubricant base oil according to thisembodiment is preferably no more than 10 mass %, more preferably no morethan 5 mass %, further preferably no more than 4 mass %, especiallypreferably no more than 3 mass %, and most preferably no more than 2mass %, on the basis of the total mass of the lubricant base oil; may be0 mass %; and is preferably no less than 0.1 mass %, more preferably noless than 0.5 mass %, further preferably no less than 1 mass %, andespecially preferably no less than 1.5 mass %. In a case where thearomatic content is beyond the above upper limit, theviscosity-temperature characteristics, thermal and oxidation stability,friction properties, and further, anti-evaporation performance and thelow-temperature viscosity properties tend to deteriorate. Further, in acase where an additive is incorporated to the lubricant base oil,effects of the additive tend to decrease. Although the lubricant baseoil according to this embodiment does not have to contain the aromaticcontent, the aromatic content no less than the above described lowerlimit makes it possible to further improve solubility of an additive.

In this specification, the aromatic content means a value measuredconforming to ASTM D 2007-93. The aromatic content usually includesalkylbenzenes, and alkylnaphthalenes; anthracenes, phenanthrenes, andalkylated compounds thereof; and compounds having four or more fusedbenzene rings, aromatic compounds having hetero atoms such as pyridines,quinolines, phenols, and naphthols.

A synthetic base oil may be used as the lubricant base oil according tothis embodiment. Examples of the synthetic base oil includepoly-α-olefins, and hydrogenated products thereof; isobutene oligomers,and hydrogenated products thereof; isoparaffins; alkylbenzenes;alkylnaphthalenes; diesters (such as ditridecyl glutarate,bis(2-ethylhexyl) azipate, diisodecyl azipate, ditridecyl azipate, andbis(2-ethylhexyl) sebacate); polyol esters (such as trimethylolpropanecaprylate, trimethylolpropane pelargonate, pentaerythritol2-ethylhexanoate, and pentaerythritol pelargonate); polyoxyalkyleneglycols; dialkyl diphenyl ethers; polyphenyl ethers; and mixturesthereof, having a kinematic viscosity of 2.0 to 5.0 mm²/s at 100° C.Among them, poly-α-olefins are preferable. Examples of poly-α-olefinstypically include oligomers and co-oligomers of C₂-C₃₂, preferablyC₆-C₁₆ α-olefins (such as 1-octene oligomers, decene oligomers, andethylene-propylene co-oligomers) and hydrogenated products thereof.

The method for producing a poly-α-olefin is not restricted. Examplesthereof include a method of polymerizing an α-olefin in the presence ofa polymerization catalyst such as a catalyst containing a complex ofaluminum trichloride or boron trifluoride, and water, alcohol (such asethanol, propanol, and butanol), a carboxylic acid or an ester.

The lubricant base oil according to this embodiment either may becomposed of one base oil component, or may contain a plurality of baseoil components, as long as the base oil as a whole has a kinematicviscosity at 100° C. of 2.0 to 5.0 mm²/s.

<(B) Metallic Detergent>

The lubricant base oil of the present invention contains (B1) acalcium-containing metallic detergent (hereinafter may be referred to as“component (B1)”) and (B2) a magnesium-containing metallic detergent(hereinafter may be referred to as “component (B2)”) as (B) a metallicdetergent (hereinafter may be referred to as “component (B)”). Examplesof the component (B) include phenate detergents, sulfonate detergentsand salicylate detergents. These metallic detergents can be used aloneor in combination.

Preferred examples of a phenate detergent include overbased salts ofalkaline earth metal salts of compounds having the structure of thefollowing formula (1). Examples of alkaline earth metals includemagnesium, barium, and calcium. Among them, magnesium and calcium arepreferable.

In the formula (1), R¹ is a C₆-C₂₁ linear or branched, saturated orunsaturated alkyl or alkenyl group; m is a polymerization degree,representing an integer of 1 to 10; A is a sulfide (—S—) group ormethylene (—CH₂—) group; and x is an integer of 1 to 3. R¹ may becombination of at least two different groups.

The carbon number of R¹ in the formula (1) is preferably 9 to 18, andmore preferably 9 to 15. If the carbon number of R¹ is less than 6, thesolubility in the base oil might be poor. On the other hand, if thecarbon number of R¹ is beyond 21, it is difficult to produce thecompound and the thermal stability might be poor.

The polymerization degree m in the formula (1) is preferably 1 to 4. Thepolymerization degree m within this range makes it possible to improvethe thermal stability.

Preferred examples of a sulfonate detergent include alkaline earth metalsalts of alkyl aromatic sulfonic acids obtained by sulfonation ofalkylaromatics, or basic or overbased salts thereof. The weight-averagemolecular weight of the alkylaromatics is preferably 400 to 1500, andmore preferably 700 to 1300.

Examples of alkaline earth metals include magnesium, barium, andcalcium, and magnesium and calcium are preferable. Examples of alkylaromatic sulfonic acids include what is called petroleum sulfonic acidsand synthetic sulfonic acids. Examples of petroleum sulfonic acids hereinclude sulfonated products of alkylaromatics of lubricant oil fractionsderived from mineral oils, and what is called mahogany acid, which is aside product of production of white oils. Examples of synthetic sulfonicacids includes a sulfonated product of alkylbenzene having a linear orbranched alkyl group, obtained by recovering side products in amanufacturing plant of alkylbenzene, which is a raw material ofdetergents, or by alkylating benzene with polyolefins. Other examples ofsynthetic sulfonic acids includes a sulfonated product ofalkylnaphthalenes such as dinonylnaphthalene. A sulfonating agent usedwhen sulfonating these alkylaromatics is not limited. For example, afuming sulfuric acid or a sulfuric anhydride can be used as thesulfonating agent.

Preferred examples of a salicylate detergent include metallicsalicylates or basic or overbased salts thereof. Preferred examples ofmetallic salicylates here include compounds represented by the followingformula (2):

In the above formula (2), each R² is independently a C₁₄-C₃₀ alkyl oralkenyl group; M is an alkaline earth metal; and n is 1 or 2. M ispreferably calcium or magnesium. Preferably n is 1. When n=2, R² may becombination of different groups.

A preferred embodiment of a salicylate detergent can be an alkalineearth metal salicylate of the above formula (2) wherein n=1, or a basicor overbased salt thereof.

A method for producing alkaline earth metal salicylate is notrestricted, and known methods for producing monoalkylsalicylates can beused. For example, an alkaline earth metal salicylate can be obtainedby: reacting a metal base such as an oxide and hydroxide of an alkalineearth metal with a monoalkylsalicylic acid obtained by alkylating aphenol as a starting material with an olefin, and then carboxylating theresultant with a carbonic acid gas or the like, or a monoalkylsalicylicacid obtained by alkylating a salicylic acid as a starting material withan equivalent of the olefin, or the like; once converting the abovemonoalkylsalicylic acid or the like to an alkali metal salt such as asodium salt and potassium salt, and then performing transmetallationwith an alkaline earth metal salt; or the like.

The metallic detergent may be overbased by a carbonate salt (forexample, an alkaline earth metal carbonate salt such as calciumcarbonate and magnesium carbonate), or a borate salt (for example, analkaline earth metal borate salt such as calcium borate and magnesiumborate).

A method for obtaining an alkaline earth metal carbonate salt-overbasedmetallic detergent is not limited. For example, such a metallicdetergent can be obtained by reacting a neutral salt of the metallicdetergent (such as an alkaline earth metal phenate, an alkaline earthmetal sulfonate, and an alkaline earth metal salicylate) with a base ofan alkaline earth metal (such as a hydroxide and an oxide of an alkalineearth metal) in the presence of carbonic acid gas.

A method for obtaining an alkaline earth metal borate salt-overbasedmetallic detergent is not limited. Such a metallic detergent can beobtained by reacting a neutral salt of a metallic detergent (such as analkaline earth metal phenate, an alkaline earth metal sulfonate, and analkaline earth metal salicylate) with a base of an alkaline earth metal(such as a hydroxide and an oxide of an alkaline earth metal) in thepresence of a boric acid or a boric acid anhydride, or a borate salt.

Examples of the component (B1) include calcium phenate detergents,calcium sulfonate detergents, calcium salicylate detergents, andcombination thereof. Preferably, the component (B1) contains at least anoverbased calcium salicylate detergent. The component (B1) may be eithercalcium carbonate-overbased, or calcium borate-overbased.

Examples of the component (B2) include magnesium phenate detergents,magnesium sulfonate detergents, magnesium salicylate detergents, andcombination thereof. Preferably, the component (B2) contains anoverbased magnesium sulfonate detergent. The component (B2) may beeither magnesium carbonate-overbased, or magnesium borate-overbased.

The metal ratio of the component (B) is a value calculated according tothe following formula; and is preferably no less than 1.0, and morepreferably no less than 1.5; and preferably no more than 10, and morepreferably no more than 3.0.

The metal ratio of the component (B)=the valence of the metal element inthe component (B)×the metal content in the component (B) (mol)/the soapgroup content of the component (B) (mol)

In a case where a boric acid salt-overbased alkaline earth metalsalicylate is contained as the component (C) described later, the metalratio of this boric acid salt-overbased alkaline earth metal salicylateis preferably no less than 1.0, and more preferably no less than 1.5;and preferably no more than 3.0, more preferably no more than 2.5, andfurther preferably no more than 2.0.

The content of the component (B) in the lubricating oil composition is,in terms of calcium on the basis of the total mass of the lubricatingoil composition, 500 to 2500 mass ppm, preferably no less than 1000 massppm, and more preferably no less than 1200 mass ppm; and preferably nomore than 2000 mass ppm, and more preferably no more than 1600 mass ppm.If the content in terms of calcium is beyond 2500 mass ppm, LSPI is easyto occur. The content in terms of calcium no less than the abovedescribed lower limit makes it possible to maintain high detergencyinside an engine, and to improve base number retention.

The content of the component (B) in the lubricating oil composition is,in terms of magnesium on the basis of the total mass of the lubricatingoil composition, 100 to 1000 mass ppm, preferably no less than 150 massppm, and more preferably no less than 200 mass ppm; and preferably nomore than 800 mass ppm, and more preferably no more than 500 mass ppm.The content in terms of magnesium no less than the above described lowerlimit makes it possible to improve detergency of an engine whilesuppressing LSPI. The content in terms of magnesium no more than theabove described upper limit makes it possible to suppress increase offriction coefficients.

<(C) Boron-Containing Additive>

The lubricating oil composition of the present invention contains (C) aboron-containing additive that is oil-soluble or oil-dispersible and isstable in oil (hereinafter may be simply referred to as “component(C)”). The component (C) may compose at least part of the component (B).

(C1) a boric acid salt-overbased metallic detergent (hereinafter may besimply referred to as “component (C1)”), and/or (C2) a boronated ashlessdispersant (hereinafter may be simply referred to as “component (C2)”)can be preferably used as the component (C). Preferably the component(C) contains at least the component (C1).

In a case where the lubricating oil composition contains the component(C1), the component (C1) composes at least part of the component (B).Examples of the component (C1) include a boric acid salt-overbasedalkaline earth metal phenate, a boric acid salt-overbased alkaline earthmetal salicylate, and a boric acid salt-overbased alkaline earth metalsulfonate. Among them, a boric acid salt-overbased alkaline earth metalsalicylate can be preferably used. The component (C1) may compose atleast part of the component (B1), or may compose at least part of thecomponent (B2), or may compose at least part of the component (B1) andpart of the component (B2), or may compose neither the component (B1)nor (B2).

Preferred examples of the component (C2) include boronated products ofnitrogen-containing ashless dispersants. Examples of nitrogen-containingashless dispersants to be boronated include at least onenitrogen-containing ashless dispersant selected from the following(C2a′) to (C2c′):

(C2a′) succinimide having at least one alkyl or alkenyl group in itsmolecule (hereinafter may be referred to as “ashless dispersant(C2a′)”);

(C2b′) benzylamine having at least one alkyl or alkenyl group in itsmolecule (hereinafter may be referred to as “ashless dispersant(C2b′)”); and

(C2c′) polyamine having at least one alkyl or alkenyl group in itsmolecule (hereinafter may be referred to as “ashless dispersant(C2c′)”).

Hereinafter a boronated product of the ashless dispersant (C2a′) may bereferred to as “component (C2a)”, a boronated product of the ashlessdispersant (C2b′) may be referred to as “component (C2b)”, and aboronated product of the ashless dispersant (C2c′) may be referred to as“component (C2c)”.

Among them, the component (C2a) can be especially preferably used.

Examples of the ashless dispersant (C2a′) include compounds representedby the following formula (3) or (4):

In the formula (3), R³ is a C₄₀-C₄₀₀ alkyl or alkenyl group; hrepresents an integer of 1 to 5, preferably 2 to 4. The carbon number ofR³ is preferably no less than 60, and preferably no more than 350.

In the formula (4), R⁴ and R⁵ are independently C₄₀-C₄₀₀ alkyl oralkenyl group, and may be combination of different groups. R⁴ and R⁵ areespecially preferably polybutenyl groups. In addition, i represents aninteger of 0 to 4, preferably 1 to 3. The carbon number of R⁴ and R⁵ ispreferably no less than 60, and preferably no more than 350.

The above lower limits or over of the carbon numbers of R³ to R⁵ in theformulas (3) and (4) make it possible to obtain good solubility in thelubricant base oil. On the other hand, the above upper limits or belowof the carbon numbers of R³ to R⁵ make it possible to improvelow-temperature fluidity of the lubricating oil composition.

The alkyl or alkenyl groups (R³ to R⁵) in formulae (3) and (4) may belinear or branched. Preferred examples thereof include branched alkylgroups and branched alkenyl groups derived from oligomers of olefinssuch as propene, 1-butene, and isobutene, or from co-oligomers ofethylene and propylene. Among them, a branched alkyl or alkenyl groupderived from oligomers of isobutene that are conventionally referred toas polyisobutylene, or a polybutenyl group are most preferable.

Preferred number-average molecular weight of the alkyl or alkenyl groups(R³ to R⁵) in formulae (3) and (4) is 800 to 3500.

Succinimide having at least one alkyl or alkenyl group in its moleculeincludes so-called monotype succinimide represented by the formula (3),where a succinic anhydride terminates only one end of a polyamine chain,and so-called bistype succinimide represented by the formula (4), wheresuccinic anhydrides terminate both ends of a polyamine chain. Thelubricating oil composition of the present invention may include eithermonotype or bistype succinimide, and may include both of them as amixture.

A method for producing a succinimide having at least one alkyl oralkenyl group in its molecule is not limited. For example, suchsuccinimide can be obtained by: reacting an alkyl succinic acid or analkenyl succinic acid obtained by reacting a compound having a C₄₀-C₄₀₀alkyl or alkenyl group with maleic anhydride at 100 to 200° C., with apolyamine. Here, examples of polyamine include diethylenetriamine,triethylenetetramine, tetraethylenepentamine, and pentaethylenehexamine.

Examples of the ashless dispersant (C2b′) include compounds representedby the following formula (5):

In the formula (5), R⁶ is a C₄₀-C₄₀₀ alkyl or alkenyl group; and jrepresents an integer of 1 to 5, preferably 2 to 4. The carbon number ofR⁶ is preferably no less than 60, and preferably no more than 350.

A method for producing the ashless dispersant (C2b′) is not limited. Anexample of such a method include: reacting a polyolefin such aspropylene oligomer, polybutene, and ethylene-α-olefin copolymer, withphenol, to give an alkylphenol; and then reacting the alkylphenol withformaldehyde, and a polyamine such as diethylenetriamine,triethylenetetramine, tetraethylenepentamine, and pentaethylenehexamine,by Mannich reaction.

Examples of the ashless dispersant (C2c′) include compounds representedby the following formula (6):

[Chem. 5]

R⁷—NH—(CH₂CH₂NH)_(k)—H  (6)

In the formula (6), R⁷ is a C₄₀-C₄₀₀ alkyl or alkenyl group; krepresents an integer of 1 to 5, preferably 2 to 4. The carbon number ofR⁷ is preferably no less than 60, and preferably no more than 350.

A method for producing the ashless dispersant (C2c′) is not limited. Anexample of such a method include: chlorinating a polyolefin such aspropylene oligomer, polybutene, and ethylene-α-olefin copolymer; andthen reacting the chlorinated polyolefin with ammonia, or a polyaminesuch as ethylenediamine, diethylenetriamine, triethylenetetramine,tetraethylenepentamine, and pentaethylenehexamine.

The components (C2a) to (C2c), that is, the boronated products of theashless dispersants (C2a′) to (C2c′) can be obtained by, for example,reacting the ashless dispersants (C2a′) to (C2c′) with boric acid, andneutralizing or amidating part or all of the residual amino groupsand/or imino groups with boric acid. Boronation may be performed incombination with modification by other reagents described below.

The content of the component (C) in the lubricating oil composition is,in terms of boron on the basis of the total mass of the lubricating oilcomposition, 50 to 1000 mass ppm, preferably no less than 190 mass ppm,more preferably no less than 270 mass ppm, and especially preferably noless than 400 mass ppm; and preferably no more than 800 mass ppm. Theboron content derived from the component (C) of the above lower limit orover makes it possible to improve fuel efficiency. The boron contentderived from the component (C) of the above upper limit or below makesit possible to maintain fuel efficiency.

In one preferred embodiment, the lubricating oil composition contains atleast the component (C1) as the component (C), and more preferably atleast a boric acid salt-overbased alkaline earth metal salicylate as thecomponent (C). The alkaline earth metal of the boric acid salt-overbasedalkaline earth metal salicylate is preferably calcium and/or magnesium.

In a case where the lubricating oil composition contains at least thecomponent (C1) as the component (C), the content of the component (C1)is, in terms of boron on the basis of the total mass of the lubricatingoil composition, preferably no less than 200 mass ppm, more preferablyno less than 300 mass ppm, and especially preferably no less than 400mass ppm; and preferably no more than 700 mass ppm. The boron contentderived from the component (C1) within the above range makes it easy toimprove fuel efficiency.

In another preferred embodiment, the lubricating oil compositioncontains the components (C1) and (C2) as the component (C). In a casewhere the lubricating oil composition contains the components (C1) and(C2) as the component (C), the content of the component (C2) is, interms of boron on the basis of the total mass of the lubricating oilcomposition, preferably no less than 50 mass ppm, and more preferably noless than 100 mass ppm; and preferably no more than 400 mass ppm. Theboron content derived from the component (C2) within the above rangemakes it easy to improve fuel efficiency.

<(D) Oil-Soluble Organic Molybdenum Compound>

The lubricating oil composition of the present invention contains (D) anoil-soluble organic molybdenum compound (hereinafter may be referred toas “component (D)”) in an amount of 100 to 2000 mass ppm in terms ofmolybdenum on the basis of the total mass of the lubricating oilcomposition. As the component (D), preferably (D1) a molybdenumdithiocarbamate (sulfurized molybdenum dithiocarbamate or sulfurizedoxymolybdenum dithiocarbamate. Hereinafter this may be referred to as“component (D1)”) is contained.

For example, a compound represented by the following formula (7) can beused as the component (D1):

In the above general formula (7), R⁸ to R¹¹ may be either the same ordifferent, and is a C₂-C₂₄ alkyl or C₆-C₂₄ (alkyl)aryl group, preferablya C₄-C₁₃ alkyl or C₁₀-C₁₅ (alkyl)aryl group. This alkyl group may be aprimary, secondary, or tertiary alkyl group, and may be linear orbranched. It is noted that “(alkyl)aryl group” means “aryl or alkylarylgroup”. In an alkylaryl group, the alkyl substituent may be in anyposition of the aromatic ring. Y¹ to Y⁴ are each independently a sulfuratom or oxygen atom. At least one of Y¹ to Y⁴ is a sulfur atom.

Examples of the oil-soluble organic molybdenum compound other than thecomponent (D1) include molybdenum dithiophosphate; complexes or the likeof a molybdenum compound (e.g. molybdenum oxides such as molybdenumdioxide and molybdenum trioxide; molybdic acids such as orthomolybdicacid, paramolybdic acid, and sulfurized (poly)molybdic acid; molybdatesalts such as metal salts and ammonium salts of these molybdic acids;molybdenum sulfides such as molybdenum disulfide, molybdenum trisulfide,molybdenum pentasulfide, and molybdenum polysulfide; sulfurized molybdicacid, and metal salts or amine salts of thereof; and molybdenum halidessuch as molybdenum chloride) and a sulfur-containing organic compound(such as alkyl (thio)xanthate, thiadiazole, mercaptothiadiazole,thiocarbonate, tetrahydrocarbyl thiuram disulfide,bis(di(thio)hydrocarbyl dithiophosphonate) disulfide, organic(poly)sulfide and sulfurized ester) or other organic compound; andsulfur-containing organic molybdenum compounds such as complexes of asulfur-containing molybdenum compound (such as the above describedmolybdenum sulfides, and sulfurized molybdic acid), and analkenylsuccinimide. These organic molybdenum compounds may be eithermononuclear molybdenum compounds, or polynuclear molybdenum compoundssuch as binuclear or trinuclear molybdenum compounds.

As the oil-soluble organic molybdenum compound other than the component(D1), an organic molybdenum compound that does not contain sulfur as aconstituent element can be used. Specific examples of such an organicmolybdenum compound that does not contain sulfur as a constituentelement include: molybdenum-amine complexes, molybdenum-succinimidecomplexes, molybdenum salts of organic acids, molybdenum salts ofalcohols, or the like. Among them, molybdenum-amine complexes,molybdenum salts of organic acids, or molybdenum salts of alcohols arepreferable.

The content of the component (D) in the lubricating oil composition is,in terms of molybdenum on the basis of the total mass of the lubricatingoil composition, 100 to 2000 mass ppm, preferably no less than 500 massppm, more preferably no less than 700 mass ppm, and especiallypreferably no less than 900 mass ppm; and preferably no more than 1500mass ppm. In a case where the content of the component (D) is less thanthe above lower limit, the effect of reducing friction by additionthereof tends to be insufficient, and fuel efficiency and thermal andoxidation stability of the lubricating oil composition tend to beinsufficient. In a case where the content of the component (D) is morethan the above upper limit, effect commensurate to the content is notobtained, and storage stability of the lubricating oil composition tendsto deteriorate.

In a case where the component (D) contains the component (D1), thecontent of the component (D1) is, in terms of molybdenum on the basis ofthe total mass of the lubricating oil composition, preferably no lessthan 300 mass ppm, more preferably no less than 500 mass ppm, furtherpreferably no less than 600 mass ppm, and especially preferably no lessthan 700 mass ppm; and preferably no more than 1200 mass ppm, and morepreferably no more than 1000 mass ppm. The molybdenum content of theabove lower limit or over makes it possible to improve fuel efficiencyand LSPI suppression performance. The molybdenum content of the aboveupper limit or below makes it possible to improve storage stability ofthe lubricating oil composition.

<Ashless Dispersant>

The lubricating oil composition of the present invention may contain anashless dispersant which falls under the above component (C) (that is,the above component (C2)), or may contain an ashless dispersant whichdoes not fall under the above component (C), or may contain boththereof. Examples of the ashless dispersant which does not fall underthe above component (C) include the above described ashless dispersants(C2a′) to (C2c′), and derivatives thereof other than the boronatedproducts of the ashless dispersants (C2a′) to (C2c′).

Examples of derivatives of the ashless dispersants (C2a′) to (C2c′)other than the boronated products include:

(i) an oxygen-containing organic compound-modified product where a partor all of the residual amino and/or imino groups is/are neutralized oramidated by reacting the ashless dispersants (C2a′) to (C2c′) with aC₁-C₃₀ monocarboxylic acid such as fatty acids, a C₂-C₃₀ polycarboxylicacid (such as ethanedioic acid, phthalic acid, trimellitic acid, andpyromellitic acid), an anhydride or ester thereof, a C₂-C₆ alkyleneoxide, or a hydroxy(poly)oxyalkylene carbonate;

(ii) a phosphoric acid-modified product where a part or all of theresidual amino and/or imino groups is/are neutralized or amidated byreacting the ashless dispersants (C2a′) to (C2c′) with phosphoric acid;and

(iii) a sulfur-modified product obtained by reacting the ashlessdispersants (C2a′) to (C2c′) with a sulfur compound.

Modification of these (i) to (iii) may be carried out in combination.

The molecular weight of the ashless dispersant is not restricted.Preferred weight-average molecular weight thereof is 1000 to 20000.

In a case where the lubricating oil composition contains the ashlessdispersant, the total content of all the ashless dispersant contained inthe lubricating oil composition is, in terms of nitrogen on the basis ofthe total mass of the lubricating oil composition, preferably no lessthan 100 mass ppm, more preferably no less than 300 mass ppm, andfurther preferably no less than 400 mass ppm; and preferably no morethan 2000 mass ppm, and more preferably no more than 1000 mass ppm,irrespective of whether or not each ashless dispersant contains boron(that is, whether or not each ashless dispersant contributes to thecontent of the component (C)). The content of all the ashless dispersantof the above lower limit or over makes it possible to sufficientlyimprove anti-coking performance (thermal stability) of the lubricatingoil composition. The content of all the ashless dispersant of the aboveupper limit or below makes it possible to maintain high fuel efficiency.

<Other Additives>

Other additives that are generally used in lubricating oils can becontained in the lubricating oil composition of the present inventionaccording to its purpose in order to further improve its performance.Examples of such additives include: zinc dialkyldithiophosphate,antioxidants, ashless friction modifiers, anti-wear additives or extremepressure agents, viscosity index improvers or pour point depressants,corrosion inhibitors, anti-rust agents, metal deactivators,demulsifiers, and anti-foaming agents.

As zinc dialkyldithiophosphate, for example, a compound represented bythe following formula (8) can be used:

In the formula (8), R¹² to R¹⁵ are independently a C₁-C₂₄ linear orbranched alkyl group, and may be combination of different groups. Thecarbon numbers of R¹² to R¹⁵ are preferably no less than 3, preferablyno more than 12, and more preferably no more than 8. R¹² to R¹⁵ may beprimary, secondary, or tertiary alkyl groups, preferably primary orsecondary alkyl groups, or combination thereof. Preferably, the moleratio of primary alkyl group and secondary alkyl group (primary alkylgroup:secondary alkyl group) is 0:100 to 30:70. This ratio may be theintramolecular combination ratio of alkyl chains, or may be the mixingratio of ZnDTP having only primary alkyl groups and ZnDTP having onlysecondary alkyl groups. When secondary alkyl groups are major, fuelefficiency can be improved.

A method for producing the above zinc dialkyldithiophosphate is notlimited. For example, zinc dialkyldithiophosphate can be synthesized by:reacting alcohol(s) having an alkyl group corresponding to R¹² to R¹⁵with phosphorus pentasulfide, to synthesize dithiophosphoric acid; andneutralizing the dithiophosphoric acid with zinc oxide.

In a case where the lubricating oil composition contains ZnDTP, thecontent thereof is, in terms of phosphorus on the basis of the totalmass of the composition, preferably no less than 600 mass ppm, morepreferably no less than 700 mass ppm, and especially preferably no lessthan 800 mass ppm; and preferably no more than 1000 mass ppm. The ZnDTPcontent of the above lower limit or over makes it possible to improvenot only oxidation stability but also LSPI suppression performance. TheZnDTP content beyond the above upper limit brings about unfavorablesignificant poisoning of an exhaust gas treatment catalyst.

Known antioxidants such as phenolic antioxidants and amine antioxidantscan be used as the antioxidant. Examples thereof include: amineantioxidants such as alkylated diphenylamine, phenyl-α-naphthylamine,and alkylated α-naphthylamine; and phenolic antioxidants such as2,6-di-t-butyl-4-methylphenol, and4,4′-methylenebis(2,6-di-t-butylphenol).

In a case where the lubricating oil composition contains an antioxidant,the content thereof is usually no more than 5.0 mass %, preferably nomore than 3.0 mass %; and preferably no less than 0.1 mass %, morepreferably no less than 0.5 mass %, on the basis of the total mass ofthe lubricating oil composition.

As the ashless friction modifier, compounds usually used as frictionmodifiers for lubricant oils can be used without particular limitation.Examples of the ashless friction modifier include C₆-C₅₀ compoundscontaining, in each of their molecules, at least one heteroatom selectedfrom the group of an oxygen atom, a nitrogen atom and a sulfur atom.More specific examples thereof include ashless friction modifiers suchas amines, fatty acid esters, fatty acid amides, fatty acids, aliphaticalcohols, aliphatic ethers, urea compounds, and hydrazide compounds,each having at least one C₆-C₃₀ alkyl or alkenyl group, especiallyC₆-C₃₀ linear alkyl, linear alkenyl, branched alkyl, or branched alkenylgroup, in each of their molecules.

In a case where the lubricating oil composition contains an ashlessfriction modifier, the content thereof is preferably no less than 0.01mass %, more preferably no less than 0.1 mass %, and further preferablyno less than 0.3 mass %; and preferably no more than 2 mass %, morepreferably no more than 1 mass %, and especially preferably no more than0.8 mass % on the basis of the total mass of the lubricating oilcomposition. The content of the ashless friction modifier of less than0.01 mass % tends to lead to insufficient friction reducing effect byaddition thereof. The content thereof beyond 2 mass % tends to inhibiteffects of anti-wear additives etc., or to deteriorate solubility ofadditives.

Anti-wear agents or extreme pressure agents used for lubricating oilscan be used as the anti-wear agent or extreme pressure agent withoutparticular limitation. Examples thereof include sulfur-based,phosphorous-based, and sulfur-phosphorous-based extreme pressure agents.Specific examples include phosphite esters, thiophosphite esters,dithiophosphite esters, trithiophosphite esters, phosphate esters,thiophosphate esters, dithiophosphate esters, trithiophosphate esters,amine salts thereof, metal salts thereof, derivatives thereof,dithiocarbamates, zinc dithiocarbamate, disulfides, polysulfides,sulfurized olefins, and sulfurized oils. Among them, addition of asulfur-based extreme pressure agent, especially a sulfurized oil ispreferable. In a case where the lubricating oil composition contains ananti-wear agent or extreme pressure agent, the content thereof ispreferably 0.01 to 10 mass % based on the total mass of the lubricatingoil composition.

Non-dispersant viscosity index improvers and dispersant viscosity indeximprovers can be used as the viscosity index improver. Specific examplesthereof include: non-dispersant or dispersant polymethacrylates, olefincopolymers, polyisobutenes, polystyrenes, ethylene-propylene copolymers,styrene-diene copolymers and hydrogenated products thereof, or the like.Their weight-average molecular weights are generally 5,000 to 1,000,000.In order to further improve the fuel efficiency, it is desirable to usethe above viscosity index improver having a weight average molecularweight of 100,000 to 1,000,000, preferably 200,000 to 900,000,especially preferably 400,000 to 800,000. In the lubricating oilcomposition of the present invention, in view of improvement of fuelefficiency, a poly(meth)acrylate viscosity index improver comprising 30to 90 mole % of the structural units represented by the followinggeneral formula (9) and 0.1 to 50 mole % of the structural unitsrepresented by the following general formula (10), wherein thehydrocarbon main chain ratio is no more than 0.18, can be especiallypreferably used. In this specification, “hydrocarbon main chain ratio”of a poly(meth)acrylate viscosity index improver means the proportion ofthe carbon number derived from the main chain to the total carbon numberof the poly(meth)acrylate viscosity index improver (the carbon number ofthe main chain/the total carbon number).

In the above general formula (9), R¹⁶ is a hydrogen atom or a methylgroup, and R¹⁷ is a linear or branched hydrocarbon group having a carbonnumber of no more than 6. In the general formula (10), R¹⁸ is a hydrogenatom or a methyl group, and R¹⁹ is a linear or branched hydrocarbongroup having a carbon number of no less than 16.

This viscosity index improver preferably has a PSSI (Permanent ShearStability Index) in a Diesel Injector method of no more than 30. If PSSIis beyond 30, shear stability is poor, and keeping a certain level orbetter of a kinematic viscosity and a HTHS viscosity of an oil after usemight sacrifice fuel efficiency at the early stage of use.

“PSSI in a Diesel Injector method” mentioned here means a permanentshear stability index of a polymer calculated based on data measuredaccording to the method specified in ASTM D6278-02 (Test Method forShear Stability of Polymer Containing Fluids Using a European DieselInjector Apparatus), conforming to ASTM D6022-01 (Standard Practice forCalculation of Permanent Shear Stability Index).

When the lubricating oil composition contains a viscosity indeximprover, the content thereof is generally beyond 0 mass % and no morethan 20 mass % on the basis of the total mass of the lubricating oilcomposition. Specific content thereof may be, for example, such contentthat the lubricating oil composition can have desirable viscosityproperties (kinematic vescocity, viscosity index, and HTHS viscosity)described below.

Examples of the pour point depressant include polymethacrylate polymers.In a case where the lubricating oil composition contains a pour pointdepressant, the content thereof is usually 0.01 to 2 mass % on the basisof the total mass of the lubricating oil composition.

Known corrosion inhibitors such as benzotriazole compounds,tolyltriazole compounds, thiadiazole compounds, and imidazole compoundscan be used as the corrosion inhibitor. In a case where the lubricatingoil composition contains a corrosion inhibitor, the content thereof isusually 0.005 to 5 mass % on the basis of the total mass of thelubricating oil composition.

Known anti-rust agents such as petroleum sulfonates,alkylbenzenesulfonates, dinonylnaphthalenesulfonates, alkylsulfonatesalts, fatty acids, alkenylsuccinimide half esters, fatty acid soaps,fatty acid polyol esters, fatty acid amine salts, oxidized paraffins,and alkyl polyoxyethylene ethers can be used as the anti-rust agent. Ina case where the lubricating oil composition contains an anti-rustagent, the content thereof is usually 0.005 to 5 mass % on the basis ofthe total mass of the lubricating oil composition.

Known metal deactivators such as imidazolines, pyrimidine derivatives,alkylthiadiazoles, mercaptobenzothiazoles, benzotriazoles and theirderivatives, 1,3,4-thiadiazole polysulfide,1,3,4-thiadiazolyl-2,5-bis(dialkyl dithiocarbamate),2-(alkyldithio)benzimidazole, and β-(o-carboxybenzylthio)propionitrilecan be used as the metal deactivator. In a case where the lubricatingoil composition contains a metal deactivator, the content thereof isusually 0.005 to 1 mass % on the basis of the total mass of thelubricating oil composition.

Known demulsifiers such as polyalkylene glycol-based nonionicsurfactants can be used as the demulsifier. In a case where thelubricating oil composition contains a demulsifier, the content thereofis usually 0.005 to 5 mass % on the basis of the total mass of thelubricating oil composition.

Known anti-foaming agent such as silicones, fluorosilicones, andfluoroalkyl ethers can be used as the anti-foaming agent. In a casewhere the lubricating oil composition contains an anti-foaming agent,the content thereof is usually 0.0001 to 0.1 mass % on the basis of thetotal mass of the lubricating oil composition.

As the coloring agent, for example, a known coloring agent such as azocompounds can be used.

<Lubricating Oil Composition>

The kinematic viscosity of the lubricating oil composition at 100° C. ispreferably 4.0 to 12 mm²/s, more preferably no more than 9.3 mm²/s,especially preferably no more than 8.5 mm²/s; and more preferably noless than 5.0 mm²/s, further preferably no less than 5.5 mm²/s,especially preferably no less than 6.1 mm²/s. In a case where thekinematic viscosity of the lubricating oil composition at 100° C. isunder 4.0 mm²/s, lubricity might be insufficient. In a case where thekinematic viscosity thereof is beyond 12 mm²/s, necessarylow-temperature viscosity and sufficient fuel efficiency might not beobtained.

The kinematic viscosity of the lubricating oil composition at 40° C. ispreferably 4.0 to 50 mm²/s, more preferably no more than 40 mm²/s,especially preferably no more than 35 mm²/s; and more preferably no lessthan 15 mm²/s, further preferably no less than 18 mm²/s, especiallypreferably no less than 20 mm²/s. In a case where the kinematicviscosity of the lubricating oil composition at 40° C. is under 4 mm²/s,lubricity might be insufficient. In a case where the kinematic viscositythereof is beyond 50 mm²/s, necessary low-temperature viscosity andsufficient fuel efficiency might not be obtained.

The viscosity index of the lubricating oil composition is preferably 140to 400, more preferably no less than 60, further preferably no less than180, especially preferably no less than 200, and most preferably no lessthan 210. In a case where the viscosity index of the lubricating oilcomposition is under 140, it might be difficult to improve fuelefficiency while keeping the HTHS viscosity at 150° C., and further, toreduce low-temperature viscosity (for example, the viscosity at −35° C.that is measurement temperature of the CCS viscosity specified in SAEviscosity grade 0W-X, known as a viscosity grade of fuel-efficientoils). In a case where the viscosity index of the lubricating oilcomposition is beyond 400, evaporation loss might deteriorate, andfurther, malfunctioning might occur due to insufficient solubility ofadditives and compatibility with sealing materials.

The HTHS viscosity of the lubricating oil composition at 100° C. ispreferably no more than 5.5 mPa·s, more preferably no more than 5.0mPa·s, especially preferably no more than 4.8 mPa·s; and preferably noless than 3.0 mPa·s, more preferably no less than 3.5 mPa·s, especiallypreferably no less than 4.0 mPa·s. In this specification, the HTHSviscosity at 100° C. indicates high temperature high shear viscosity at100° C., specified in ASTM D4683. In a case where the HTHS viscosity at100° C. is under 3.0 mPa·s, lubricity might be insufficient. In a casewhere the HTHS viscosity at 100° C. is beyond 5.5 mPa·s, necessarylow-temperature viscosity and sufficient fuel efficiency might not beobtained.

The HTHS viscosity of the lubricating oil composition at 150° C. ispreferably no more than 2.7 mPa·s, more preferably no more than 2.4mPa·s; and preferably no less than 1.9 mPa·s, more preferably no lessthan 2.1 mPa·s. In this specification, the HTHS viscosity at 150° C.indicates high temperature high shear viscosity at 150° C., specified inASTM D4683. In a case where the HTHS viscosity at 150° C. is under 1.9mPa·s, lubricity might be insufficient. In a case where the HTHSviscosity at 150° C. is beyond 2.7 mPa·s, fuel efficiency might beinsufficient.

The evaporation loss of the lubricating oil composition is, as NOACKevaporation loss at 250° C., preferably no more than 30 mass %, furtherpreferably no more than 20 mass %, and especially preferably no morethan 15 mass %. In a case where the NOACK evaporation loss of thelubricating oil composition is beyond 30 mass %, the evaporation loss ofthe lubricating oil is large, which causes viscosity increase and thelike, and is thus unfavorable. In this specification, the NOACKevaporation loss is evaporation loss of the lubricating oil measuredconforming to ASTM D 5800. The lower limit of the NOACK evaporation lossof the lubricating oil composition at 250° C. is not restricted, butnormally no less than 5 mass %.

The mass ratio (MB/Mg) of the boron content (MB) to the magnesiumcontent (Mg) in the lubricating oil composition is 0.5 to 10, preferablyno less than 0.8, and preferably no more than 8. The mass ratio MB/Mg ofthe above lower limit or over makes it possible to improve fuelefficiency. The mass ratio MB/Mg of the above upper limit or below makesit possible to maintain fuel efficiency.

The lubricating oil composition of the present invention satisfies atleast one of the following requirements (i) to (iii):

(i) the boron content in the composition is no less than 270 mass ppm onthe basis of the total mass of the composition;

(ii) the component (C) contains a boric acid salt-overbased metallicdetergent (that may compose at least a part of the component (B1) and/orthe component (B2)); and

(iii) the mass ratio (MB/Mg) of the boron content (MB) to the magnesiumcontent (Mg) in the composition is no less than 0.8.

Satisfying at least one of the above requirements (i) to (iii) makes itpossible to improve fuel efficiency.

EXAMPLES

Hereinafter the present invention will be more specifically describedbased on examples and comparative examples. It is noted that the presentinvention is not limited to these examples.

Examples 1 to 8 and Comparative Examples 1 to 5

Each of the lubricating oil compositions of the present invention(examples 1 to 8) and the lubricating oil compositions for comparison(comparative examples 1 to 5) was prepared using the following base oiland additives. Formulation of each composition is shown in Table 2. InTable 2, “mass %” means mass % on the basis of the total mass of eachcomposition, “mass ppm” means mass ppm on the basis of the total mass ofeach composition, and “mass ratio” means a ratio by mass.

(Base Oil) A-1: a hydrocracked base oil having properties shown inTable 1. In Table 1, “mass ppm” means mass ppm on the basis of the totalmass of the base oil, and “mass %” means mass % on the basis of thetotal mass of the base oil.

TABLE 1 Properties Unit Value Density (15° C.) g/cm³ 0.820 KinematicViscosity (40° C.) mm²/s 17.8 Kinematic Viscosity (100° C.) mm²/s 4.07Viscosity Index 132 Pour Point ° C. −22.5 Aniline Point ° C. 119 IodineNumber 0.05 S Content mass ppm <1 N Content mass ppm <3 n-d-M Analysis %C_(P) 87.3 % C_(N) 12.7 % C_(A) 0 Chromatographic Analysis SaturatedContent mass % 99.6 Aromatic Content mass % 0.2 Resin Content mass % 0.2Recovery Rate mass % 100

(Metallic Detergents)

B1-1: calcium carbonate-overbased calcium salicylate, Ca content: 6.2mass %, metal ratio: 2.3, alkyl chain length: 14-18, base number(perchloric acid method): 180 mgKOH/g.

B1-2 (C1): calcium borate-overbased calcium salicylate, Ca content: 6.8mass %, boron content: 2.7 mass %, metal ratio: 2.5, and base number(perchloric acid method): 190 mgKOH/g.

B1-3 (C1): calcium borate-overbased calcium salicylate, Ca content: 5.0mass %, boron content: 1.8 mass %, metal ratio: 1.5, base number(perchloric acid method): 140 mgKOH/g.

B2-1: magnesium carbonate-overbased magnesium sulfonate, Mg content: 9.5mass %, base number (perchloric acid method): 400 mgKOH/g, sulfurcontent: 2 mass %.

(Ashless Dispersants)

C₂a′-1: polybutenylsuccinimide, Mw: 9000, nitrogen content: 0.7 mass %boron content: 0 mass %.

C₂a-1: boronated polybutenylsuccinimide, Mw: 6000, nitrogen content: 1.6mass % boron content: 0.5 mass %.

(Oil-Soluble Organic Molybdenum Compounds)

D-1: sulfurized (oxy)molybdenum dithiocarbamate

D-2: Mo-based anti-oxidant

(Viscosity Index Improver)

E-1: non-dispersant polymethacrylate viscosity index improver, in weightaverage molecular weight: 400,000, PSSI: 25

(Other Additives)

F-1: additive mixture containing a zinc dialkyl dithiophosphate, anashless anti-oxidant, and a anti-foaming agent.

Examples 1 2 3 4 5 6 7 Base oil A-1 balance balance balance balancebalance balance balance Metallic detergents B1-1 mass % — — — — 0.6 1.5— B1-2(C1-1) mass % 2.3 — 2.3 1.7 1.7 0.8 2.3 B1-3(C1-2) mass % — 2.9 —— — — — B2-1 mass % 0.2 0.2 0.08 0.4 0.2 0.3 0.2 Ashless dispersantsC2a′-1 mass % 3.2 3.2 3.2 3.2 — 3.2 3.2 C2a-1 mass % — — — — 3.0 — —Oil-soluble organic Mo compounds D-1 (in terms of Mo) mass ppm (800)(800) (800) (800) (800) (800) (800) D-2 (in terms of Mo) mass ppm (200)(200) (200) (200) (200) (200) (200) Total Amount (D-1 + D-2) mass % 1.51.5 1.5 1.5 1.5 1.5 1.5 Viscosity index improver E-1 mass % 5.3 5.3 5.35.3 5.3 5.3 7.7 Other additives F-1 mass % 2.4 2.4 2.4 2.4 2.4 2.4 2.4Kinematic viscosity 40° C. mm²/s 26.4 26.5 26.5 26.5 26.5 26.5 28.7 100°C. mm²/s 6.5 6.5 6.5 6.5 6.5 6.5 7.7 Viscosity index 214 214 214 214 214214 235 HTHS Viscosity 100° C. mPa · s 4.5 4.5 4.5 45 4.5 4.5 4.8 150°C. mPa · s 2.3 2.3 2.3 2.3 2.3 2.3 2.6 NOACK evaporation loss (250° C.,1 mass % 12 12 12 12 12 12 12 Elements in Oil Ca mass ppm 1600 1600 16001200 1600 1500 1600 B mass ppm 600 500 600 450 600 200 600 Mg mass ppm240 240 100 500 240 350 240 Mo mass ppm 1000 1000 1000 1000 1000 10001000 B/Mg mass ratio 2.5 2.1 6 0.9 2.5 0.6 2.5 Stand-alone valve-trainlest Torque reduction (vs. Comp. Ex. % 2.8 5.2 2.2 2.0 1.5 0.9 2.8Motoring ergine torque test Torque reduction (vs. Comp. Ex. % 2.4 — — —— — 1.6 Examples Comparative examples 8 1 2 3 4 5 Base oil A-1 balancebalance balance balance balance balance Metallic detergents B1-1 mass %— 2.4 3.1 1.8 2.2 1.8 B1-2(C1-1) mass % 2.3 — — — 0.2 0.8 B1-3(C1-2)mass % — — — — — — B2-1 mass % 0.2 0.2 — 0.4 0.2 0.7 Ashless dispersantsC2a'-1 mass % 3.2 3.2 3.2 3.2 3.2 3.2 C2a-1 mass % — — — — — —Oil-soluble organic Mo compounds D-1 (in terms of Mo) mass ppm (800)(800) (800) (800) (800) (800) D-2 (in terms of Mo) mass ppm (200) (200)(200) (200) (200) (200) Total Amount (D-1 + D-2) mass % 1.5 1.5 1.5 1.51.5 1.5 Viscosity index improver E-1 mass % — 5.3 5.3 5.3 5.3 5.3 Otheradditives F-1 mass % 2.4 2.4 2.4 2.4 2.4 2.4 Kinematic viscosity 40° C.mm²/s 19 26.5 26.4 36.4 26.5 26.5 100° C. mm²/s 4.9 6.5 6.5 6.5 6.5 6.5Viscosity index 151 214 214 215 214 214 HTHS Viscosity 100° C. mPa · s3.9 4.5 4.5 4.5 4.5 4.5 150° C. mPa · s 1.9 2.3 2.3 2.3 2.3 2.3 NOACKevaporation loss (250° C., 1 mass % 12 12 12 12 12 12 Elements in Oil Camass ppm 1600 1600 1600 1200 1600 1600 B mass ppm 600 0 0 0 30 150 Mgmass ppm 240 240 0 500 150 700 Mo mass ppm 1000 1000 1000 1000 1000 1000B/Mg mass ratio 2.5 0 0 0 0.2 0.2 Stand-alone valve-train lest Torquereduction (vs. Comp. Ex. % 2.9 reference −0.8 0.0 −2.1 −3.0 Motoringergine torque test Torque reduction (vs. Comp. Ex. % 4.8 reference — — ——

(Stand-Alone Valve-Train Test)

For each lubricating oil composition of examples 1 to 8 and comparativeexamples 1 to 5, low friction performance was evaluated by a valve-trainsystem motoring friction test machine.

A valve-train system motoring friction test machine is a device whichcan measure friction torque of a pair of a cam and a tappet in avalve-train system of a direct acting engine. Friction torque at 80° C.in oil temperature at 350 rpm in rotation frequency was measured whilethe machine was lubricated by each lubricating oil composition. Then,the torque reduction rate compared to the measurement value in thecomparative example 1 was calculated. As the reduction rate is higher,fuel efficiency is better. Results are shown in Table 2.

(Motoring Engine Torque Test)

For each lubricating oil composition of examples 1, 7 and 8 andcomparative example 1, a motoring engine torque test was further carriedout. For each lubricating oil composition, torque necessary for rotatingan output shaft of a DOHC engine (displacement: 2 L) by an electricmotor at certain rotation frequency was measured, while the engine waslubricated by each lubricating oil composition (oil temperature: 80°C.). The measurement was performed at 1400 rpm, and the torque reductionrate compared to the measurement value in the comparative example 1 wascalculated. As the torque reduction rate is higher, fuel efficiency isbetter. Results are shown in Table 2.

INDUSTRIAL APPLICABILITY

The lubricating oil composition of the present invention makes itpossible to secure LSPI suppression performance and detergency, and toimprove fuel efficiency at the same time. Thus, the lubricating oilcomposition of the present invention can be preferably used forlubrication of turbocharged gasoline engines, especially turbochargeddirect injection engines, which is apt to suffer LSPI problems.

1. A lubricating oil composition for an internal combustion engine, thecomposition comprising: (A) a lubricant base oil having kinematicviscosity at 100° C. of 2 to 5 mm²/s; (B) a metallic detergent in anamount of 500 to 2500 mass ppm in terms of calcium and 100 to 1000 massppm in terms of magnesium, on the basis of the total mass of thecomposition, the metallic detergent comprising both (B1) acalcium-containing metallic detergent and (B2) a magnesium-containingmetallic detergent; (C) a boron-containing additive in an amount of 50to 1000 mass ppm in terms of boron on the basis of the total mass of thecomposition, wherein the boron-containing additive is oil-soluble oroil-dispersible and is stable in oil, and wherein the boron-containingadditive may compose at least a part of the component (B); and (D) anoil-soluble organic molybdenum compound in an amount of 100 to 2000 massppm in terms of molybdenum on the basis of the total mass of thecomposition, wherein a mass ratio (MB/Mg) of boron content of thecomposition (MB) to magnesium content of the composition (Mg) is 0.5 to10; and the composition satisfies one or more requirement selected fromthe following (i) to (iii): (i) the boron content of the composition isno less than 270 mass ppm on the basis of the total mass of thecomposition; (ii) the component (C) comprises a boric acidsalt-overbased metallic detergent, wherein the boric acid salt-overbasedmetallic detergent may compose at least a part of the component (B1) orthe component (B2) or the combination thereof; and (iii) the mass ratio(MB/Mg) of the boron content of the composition (MB) to the magnesiumcontent of the composition (Mg) is no less than 0.8.
 2. The lubricatingoil composition according to claim 1, wherein the component (C)comprises a boric acid salt-overbased alkaline earth metal salicylate.3. The lubricating oil composition according to claim 1, wherein thecomponent (B) comprises an overbased magnesium sulfonate.
 4. Thelubricating oil composition according to claim 1, wherein the component(D) comprises a molybdenum dithiocarbamate in an amount of 100 to 2000mass ppm in terms of molybdenum on the basis of the total mass of thecomposition.
 5. The lubricating oil composition according to claim 1,wherein the composition has HTHS viscosity at 150° C. of 1.9 to 2.7mPa·s.
 6. The lubricating oil composition according to claim 1, whereinthe composition has HTHS viscosity at 150° C. of 1.9 to 2.4 mPa·s. 7.The lubricating oil composition according to claim 1, wherein thecomposition has a NOACK evaporation loss at 250° C. of no more than 15mass %.